In a hard disk drive, data on a disk is read and written by a magnetic head. To increase the recording capacity per unit area of a magnetic disk, the areal density must be increased. However, in the current longitudinal magnetic recording systems, if the recorded bit length is reduced, the areal density cannot be increased because of thermal fluctuation of the magnetization of the medium. One approach to solving this problem is the perpendicular magnetic recording method which records a magnetization signal in the direction perpendicular to the medium. In the perpendicular magnetic recording method, a giant magneto-resistive (GMR) head, and a tunneling magneto-resistive (TMR) head whose read output is large or a current perpendicular to the plane (CPP) type GMR head, are used for reading. A single pole head is used for writing.
In perpendicular magnetic recording, to increase areal density, the track density and linear recording density must be increased. To increase linear recording density, the magnetic field gradient of a recording head must be improved. For this purpose, the recording medium is divided into two layers with a soft under layer (SUL) as the lower layer. However, to increase a higher recording density exceeding 200 Gb/in2, a further improvement of magnetic field gradient from the recording head is required. In order to improve this magnetic field gradient, a trailing shield is effective, but the gap length on the trailing side must be precisely controlled. Also, to increase the track density, the track width of the head must be processed finer and more precise, but as the track becomes narrower, the effective track width written on the medium becomes significantly larger than the physical track width, so the narrowing track width had formed a greatest bottleneck to obtain track density increase. To solve this problem, for example, in US2002/0176214A1 or the point No. E6 of The Magnetic Recording Conference (TMRC) 2003, an example of a perpendicular magnetic recording head provided with a side shield, is disclosed. Also, in JP 2000-92929 A, a head provided with a trailing side shield and its manufacturing method are disclosed.